Preheat the oven to 400°F (200°C).
Place the duck in a roasting pan.
Season well with salt and pepper, and bake for 10 minutes.
Reduce the temperature of the oven to 325°F (160°C) and bake for 1 hour.
In a saucepan, mix together the orange marmalade, orange juice, water and white wine.
Bring to a boil and remove from the stove.
Remove the duck from the oven and baste the duck with the sauce.
Place the orange slices on the duck and bake for 10 minutes.
Baste a few more times during cooking.
When ready to serve, place the duck on a platter and garnish with fresh watercress.
Accompany with the sauce in a gravy boat.